The storage of gases and liquids in solution mined salt caverns, whether leached in domal or stratified salt formations can result in contamination of the stored product by, for example, egress of impurities from the salt formation and overburden outside the salt formation. The stored products typically include hydrogen, nitrogen, carbon dioxide, air, methane, ethane, ethylene, propylene, propane, ethane/propane mix (LPG), butane, or pentane.
Typical impurities include, but are not limited to, hydrogen sulfide (H2S), methane (CH4), carbon dioxide (CO2), nitrogen (N2), ethane (C2H6), benzene (C6H6) and other naturally occurring hydrocarbons (CxHx). These impurities were found to enter the salt cavern from two sources, either gas bubbles trapped in the salt formation or methane gas entering the cavern through fractures and weak seams.
In a single cavern storage configuration, it was found that impurities accumulate in the stored product and increase over time, causing the product to not meet commercial specification.